Here are a few tips that I've found helpful when I sit down to write about a book. Give them a try!

Before you begin writing, make a few notes about the points
you want to get across.

While you're writing, try thinking of your reader as a friend
to whom you're telling a story.

Try to mention the name of the author and the book title in
the first paragraph  there's nothing more frustrating than
reading a review of a great book but not knowing who wrote it
and what the title is!

If possible, use one paragraph for each point you want to make
about the book. It's a good way to emphasize the importance of
the point. You might want to list the main points in your notes
before you begin.

Try to get the main theme of the book across in the beginning
of your review. Your reader should know right away what he or
she is getting into should they choose to read the book!

Think about whether the book is part of a genre. Does the book
fit into a type like mystery, adventure, or romance? What aspects
of the genre does it use?

What do you like or dislike about the book's writing style?
Is it funny? Does it give you a sense of the place it's set? What
is the author's/narrator's "voice" like?

Try using a few short quotes from the book to illustrate your
points. This is not absolutely necessary, but it's a good way
to give your reader a sense of the author's writing style.

Make sure your review explains how you feel about the book
and why, not just what the book is about. A good review should
express the reviewer's opinion and persuade the reader to share
it, to read the book, or to avoid reading it.

Do research about the author and incorporate what you learn
into the review. Biographical information can help you formulate
your opinion about the book, and gives your review a "depth."
Remember, a book doesn't come directly from a printing press,
it's a product of an author's mind, and therefore it may be helpful
to know something about the author and how she or he came to write
the book. For instance, a little research will reveal the following
about author Harper Lee:

To Kill a Mockingbird, which won the Pulitzer Prize,
is the only book she's ever published.

The town she called Maycomb is really Monroeville, Alabama.
Many of the residents thought the author had betrayed them by
writing the book.

Some people think she based the character Dill on Truman Capote,
a famous writer who was her childhood friend.